That's what it says on the new notes regarding the Free Character Migration. I wish to move from Stormscale Horde (long que times) to Talnivarr, I can only choose Ravencrest which is a heavy populated realm with close to 0 hordeplayers. Will there be a way to migrate to talnivarr, shattered halls, chromaggus, boulderfist or daggerspine?

We carefully select which realms to have as destinations for FCMs, and this time we opened up the offer to Alliance players on Stormscale as well as Horde to help reduce the queue. We'll re-assess the situation at a later date and adjust the FCMs if queues are still persistent.

We alter the destination realms based on different factors, so unfortunately it's not possible to say whether or not the realms you mentioned may be chosen in the future.